1. Field of the Invention
The present invention relates generally to a zoom lens for optical equipment such as a camera, a camera-equipped mobile phone and a projector and more particularly, to a zoom lens which is durable in use and easy in manufacturing.
2. Description of the Related Art
To fit the trend of creating electronic products having light, thin, short and small characteristics, parts for electronic products must be small-sized. For example, a zoom lens for mobile phone must be small sized for easy installation in a mobile phone for saving space. A conventional zoom lens for mobile phone generally comprises a housing, a rotatable adjustment member mounted in the housing, and a lens barrel coupled to the rotatable adjustment member. When adjusting the focal length of the zoom lens, the user must rotate the rotatable adjustment member to move the lens barrel forwards or backwards in an axial direction. This design of such zoom lens further comprises a cylindrical spiral coil spring supported between the housing and the rotatable adjustment member to stabilize movement of the rotatable adjustment member, ensuring accurate adjustment of the focal length.
Because the spiral coil spring is made by winding a resilient metal wire into shape, the change between the axial length and volume of the spiral spring before and after compression is not drastic when the rotatable adjustment member is moved to compress or stretch the spiral coil spring. Because of a small compression ratio, the spiral coil spring occupies a big space in the zoom lens, resulting in a barrier to the development of a miniature zoom lens structure. Furthermore, except the requirement for high precision, the parts of a focal length-adjustable lens must be stable and durable. However, when the user rotates the rotatable adjustment member to adjust the focal length of the zoom lens, the end of the spiral coil spring connected to the rotatable adjustment member is synchronously rotated with the rotatable adjustment member, thereby causing stretch and even deformation of the spiral coil spring. When the spiral coil spring is deformed, it is unable to ensure uniform pressure application, thereby resulting in unsmooth operation of the zoom lens and friction of parts. Frequent friction of the parts will shorten the service life of the zoom lens.